Correlation processor

ABSTRACT

Each jamming target transmits a broadband noise that is uncorrelated with any other jaming target. The noise that each target transmits is received by a monopulse radar antenna on a missile and is retransmitted to the ground processor by that missile. The ground processor also receives directly the energy from the jamming targets. Use is made of the different signal paths of each jamming target to the missile and to the processor to obtain a correlation function for each target, by delaying the direct signal to the processor and mixing it with the signal from the missile so as to maximize the mixer&#39;&#39;s output for a selected target.

Unite States ate Heminway et al.

CORRELATION PROCESSOR Inventors: John R. Heminway, Topsfield;

Herbert M. Sanborn, Framingham, both of Mass.

Assignee: The United States of America as represented by the Secretaryof the Army, Washington, DC.

Filed: Sept. 4, 1973 Appl. No.: 392,914

[52] US. Cl 343/18 E; 235/181; 343/100 CL [51] Int. Cl. G01s 7/36 [58]Field of Search 343/18 E, 100 CL; 235/181 [56] References Cited UNITEDSTATES PATENTS 3,134,896 5/1964 Briggs 343/100 CL X 3,195,130 7/1965Adrian 343/100 CL X 3,212,091 10/1965 Bissett et al. 343/100 CL X3,502,989 3/1970 Honciser .1 343/100 CL X Primary Examiner-T. H.Tubbesing Attorney, Agent, or Firm-Robert P. Gibson; Nathan Edelberg;Robert C. Sims [57] ABSTRACT Each jamming target transmits a broadbandnoise that is uncorrelated with any other jaming target. The noise thateach target transmits is received by a monopulse radar antenna on amissile and is retransmitted to the ground processor by that missile.The ground processor also receives directly the energy from the jammingtargets. Use is made of the different signal paths of each jammingtarget to the missile and to the processor to obtain a correlationfunction for each target, by delaying the direct signal to the processorand mixing it with the signal from the missile so as to maximize themixers output for a selected target.

6 Claims, 8 Drawing Figures JAMMING TARGET "I l JAMMING '7 TARGET *2STEERING COMMANDS TO MISSILE CORRELATOR PROCESSOR PATENTEDJUL 2 2 I975SHEET JAMMING STEERING COMMANDS TO MISSILE TARGET t I JAMMING TARGET #2coRRELAToR PRocEssoR COMPUTER FIG. I

I5 ARA FROM MIXER MISSILE T LOCAL 23 24 25 BAND OUTPUT OSCILLATORPRODUCT PASS DETECTOR DETECTOR F|| TER l8 2| NE HZ MIXER VARIABLE FROMDELAY TARGETS LINE (T) VOLTAGE /|9 CONTROLLED CRYSTAL OSCILLATOR 3 FIG.3 I: /-JAMMERH /-JAMMER#2 a OUTPUT OUTPUT 2 2 Q '3 .J LU O: a: L o

DELAY (T) FIG. 2

PATENTEDJUL 2 2 ms /l8 /2l QZEZ VARIABLE FROM-# MIXER DELAY v TARGETSLINE VOLTAGE CONTROLLED OSCILLATOR 3D 29 28 f2? I DETECTOR FILTERPRODUCT DELAY DETECTOR Td l V I DIFFERENTIAL/32 MISSILE FIER SUM I AMPU30' 29' 28' S'GNAL f T y I Q DETECTOR Fl T R PRODUCT I L E DETEcToRRANGE LOOP FIG. 4

VOLTAGE AMPLITUDE (VOLTS) I Td/2 +Td 2 RANGE DELAY FIG. 5

PATENTEDJUL 2 2 I975 SHEET 3 33 f 34 f 35 f 36 SUM a J DELTA DELAYPRODUCT ggg g SIGNAL FRoM DETECTOR FILTER MISSILE 38 39 LOCAL PHASE D.C.

INTEGRATOR oScILLAToR DETEcT c uTPu' SUM 33' 34' 35' 3e' SIGNAL DELAYPRODUCT Egg? FRoM MISSILE T 2 DETECTOR FILTER voLTAGE CONTROLLEDoscILLAToR 2] l8 DIRECT SIGNAL VARIABLE FROM DELAY TARGETS FIG. 6

ouTPuT 33' 34' 35' 4o SUM SIGNAL DELAY PRODUCT Q 39 FRoM MISSILE H 2DETECTOR FILTER LocAL oscILLAToR 2| DIREcT SIGNAL VARIABLE FROM DELAYTARGET LINE voLTAGE CONTROLLED INTEGRAToR A FREQUENCY oScILLAToRDIScRIMINAToR FIG. 7

CORRELATION PROCESSOR SUMMARY OF THE INVENTION The correlator processorhas two major inputs. One input comes directly from the jamming targetsthe other input comes from a missile which is to home in on one of thejamming targets. These inputs are reduced in frequency by mixers andoscillators and fed through a product detector where they are combined.Since the target path from the jamming target directly to the correlatoris shorter than the path of the jamming target to the missile and thento the correlator path, a variable delay line is inserted between thedirect signals to the product detector. By varying this delay line theoutput of the product detector can be enhanced to a peak value for asingle jammers output. The computer or operator will initially set thevariable delay line so that one ofthe jammers output is selected. Inorder to keep this variable delay line adjusted on the selected jammeras it moves in range relative to the correlator and the missile, a rangeloop is provided to adjust the variable delay line. The range loopconsists essentially of two product detectors with one of the detectorsbeing fed the output of the variable delay line directly and the otherdetector being fed the output of variable delay line through a furtherdelay means. The sum signals from the antenna of the missile are alsofed to the product detector. The outputs of the product detector are fedto a differential amplifier which compares the two outputs and generatesan error signal to control the variable delay line.

The mixer for the direct signal from the target is fed a voltage from avoltage controlled crystal oscillator. The frequency output of thisoscillator is controlled in order to compensate for the differentialdoppler frequency difference between the direct and indirect jammingtarget signal paths. This is done by introducing a delay in the outputof the direct signals and sending the output of the product detectorsthrough a narrow bandpass filter to a frequency discriminator whoseoutput voltage will be proportional to the frequency tracking error.This output is fed to the voltage control oscillator to control thefrequency output thereof.

Now the boresight error can be generated by the correlator processor byfeeding both the sum and the delta signals from the monopulse antenna ofthe missile through two channels each comprising the series circuit of amixer, delay line, and product detector. Each product detector is alsofed the direct signal from the target. The outputs of the two channelsare fed to a phase detector. Difference in the phase will indicate aboresight error with respect to the jamming target being tracked. Thiserror is sent to the computer which sends a signal to a steering antennawhich transmits a signal to the missile to cause the missile to alignupon the selected jamming target.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing thebroad overall configuration of the present invention;

FIG. 2 is a waveform showing the correlator output for two targets;

FIG.'3 is a block diagram showing one of the basic fundamental of theinvention;

FIG. 4 is a block diagram showing how the invention corrects for rangeerrors;

FIG. 5 is a waveform showing the output of the differential amplifier ofFIG. 4;

FIG. 6 is a block diagram showing the basic system for obtainingboresight error;

FIG. 7 is a block diagram showing the basic system for compensation fordifferential doppler effect; and

FIG. 8 is a block diagram showing the complete correlator system.

DESCRIPTION OF THE PREFERRED EMBODIMENT The missile-target-processorgeometry for the present invention is shown in FIG. 1, for two jammingtargets. Each target transmits a broadband noise that is not correlatedwith the noise radiated by any other jamming target or targets. Twoinput signals are applied to the signal processor 5. One of the inputsignals to the processor is the jamming noise received by the missilesseeker monopulse antenna 7 from each target. This signal isretransmitted by the missile to the ground receiver antenna 9. Thisinput signal is called the indirect input signal to the processor andconsists of two signals: the sum and the sum plus J Delta, The otherinput signal to the processor is the energy received directly from eachjamming target received by antenna 11 and is called the direct inputsignal to the processor.

From FIG. 1, it can be seen that the indirect input signals to theprocessor undergo a larger propagation delay than the direct inputsignal. That is, for target I, the indirect path signal'undergoes apropagation delay proportional to the sum of the missile-to-target pathlength L and the missile-to-receiver path length L while the direct pathsignal undergoes a propagation delay proportional to thetarget-to-receiver path length L The sum of the indirect signal pathlengths (1 L is greater than the direct signal path length (LCorrespondingly for target 2, the sum of the missile-to-target pathlength L, and the missile-to-receiver path length L is greater than thetarget-to-receiver path length L3 By placing a variable delay line inthe signal processing of the direct path signal and cross-correlatingthat delayed direct path signal with the indirect path signal, an outputsignal voltage vs delay time T in the direct path signal similar to thatshown in FIG. 2 is obtained. The details are set forth later. The peakof the crosscorrelation function obtained for target I, would occur whenthe delay placed in the direct path signal T was equal to The peak ofthe cross-correlation function obtained for target 2, would occur whenthe delay time placed in the direct path signal, T was equal to C speedof light. A plurality of targets can be discriminated using thistechnique for the signal processing through their differences indifferential propagation delay time.

The complete correlation signal processor is made up of three functions;namely, range (delay) tracking,

doppler tracking and boresight angle processing. These three functionswill be explained individually using FIGS. 3-7. Then an explanation ofhow the functions are combined will be given using FIG. 8.

A functional block diagram for the signal processing needed to obtainthe correlation output signal shown in FIG. 2 is shown in FIG. 3. FIG. 3shows the signal received from the missile is applied to a mixer whereit is frequency translated to a lower IF frequency determined by thelocal oscillator 16. The signal received directly from the targets isalso applied to a mixer 18 and frequency translated to a lower IFfrequency determined by the voltage controlled crystal oscillator (VCXO)l9 and then applied to variable delay line 21. The output signal fromthe variable delay line is multiplied or mixed by product detector 23with the frequency translated signal from the missile. The mixer outputis applied to a narrow band pass filter 24 whose output is applied todetector 25. By observing the detector output voltage as a function ofdelay time in the processor, a waveform like that shown in FIG. 2 willbe produced.

After target discrimination is accomplished, one of the targets may beselected for the missile to home on. The selection process is completedby setting the variable delay line in the processor such that thecrosscorrelation function of the selected target is peaked at theprocessor output. To maintain this correlation peak at the processoroutput, the differential time delay between the direct and indirect pathsignals for the selected target is tracked within the signal processorusing the range tracking mechanization as shown in FIG. 4.

The variable delay line 21 plus the blocks shown outlined in FIG. 4 makeup a range (delay) tracking loop. This loop automatically positionsvariable delay line 21 to the proper position to maximize the selectedtarget signal. One side of the loop is composed of a short delay line 27whose delay is Td seconds. The delay line is followed by a productdetector 28, bandpass filter 29, and an envelope detector 30. The otherside is identical except delay Td is omitted. Therefore, at thedifferential amplifier input, two correlations displaced by Td secondsare available. These are subtracted in differential amplifier 32 formingan early-late range (delay) error signal as shown in FIG. 5. When theoutput voltage from the differential amplifier 32 is zero voltage, thetwo cross-correlation signals obtained for the selected target areidentically displaced from the correlation peak of the selected target.That is, assuming the correlation peak occurs at T seconds, onecorrelation signal obtained in the range tracking loop would be at TTd/2 signals, and the other correlation signal obtained in the rangetracking loop would be at T Td/Z seconds. When the setting of thevariable delay line in the signal processor is incorrect, so that thedelay time was not set at T seconds, the output voltage fromdifferential amplifier 32 in the range tracking loop would not be zerovoltage but would be a voltage proportional to the error in the delaytime setting in the processor. The error voltage developed in the rangetracking loop as a function of the delay time setting error is shown inFIG. 5. This error voltage developed is then used to command variabledelay line 21 in the processor to its proper setting.

Guidance information for the missile about a particular jamming targetin the presence of several jamming targets is developed by processingthe monopulse signals developed in the missiles seeker antenna as shownin FIG. 6. Two identical channels are shown each having a mixer 33,small delay means 34, product detector 35, and bandpass filter 36. Theinput to one channel is the missile sum (2) signal, while the otherchannel receives the sum J delta (2 JA) signal. Both product detectors35 and 35' receive input from the variable delay line 21. Phase detector38 in FIG. 6 compares the phase of the E to the 2 .IA correlation signaland applies this to integrator 39. The monopulse signals developed inthe missiles seeker antenna are the E and 2 JA signals. For each jammingsignal received by the missiles seeker antenna, the boresight headingerror to the jamming target is proportional to the phase differencebetween the E and the Z .IA signals. The phase detector output voltageis a voltage proportional to the targets boresight error.

To minimize angle measurement noise caused by the presence of otherjamming targets, the narrowband filters 36 and 36' before the phasedetector must be kept as narrow as possible. To accomplish this, thedifferential doppler frequency between the direct and indirect pathsignals is tracked within the doppler tracking loop of the processor.The mechanization for tracking the differential doppler frequency isshown in FIG. 7. As before, the indirect path signal from the missile isfrequency translated to an IF frequency by mixing it with the crystaloscillator. The mixer output is delayed by Td/2 seconds by delay means34. The direct path input signal to the processor is frequency shiftedby mixing it with a voltage controlled crystal oscillator 19. Mixer 18output is applied to the variable delay line whose delay is set suchthat the correlation function obtained for the particular target ispeaked at the processor output. The delayed direct path signal is thenmixed with the indirect path signal and applied to a bandpass filter 40as shown in FIG. 7. The filter output is then applied to a frequencydiscriminator 41 whose output voltage is proportional to the dopplerfrequency tracking error. The discriminator output is integrated byintegrator 43 and applied to the voltage controlled oscillator 19 tocorrect same.

FIG. 8 indicates how the sub-systems, previously described in detail inFIGS. 1-7 are connected together to form the complete correlationguidance system. The desired output is the boresight error output.However, before reliable information is present here, the doppler andrange loop must be used to select one of the targets to be designated asthe tracked target. Once the doppler and range loop are locked on thattarget, the signal out of the boresight channel is proportional to angleof the missile seeker off boresight.

A step by step operational description of the overall correlatormechanism shown in FIG. 8 is given:

1. Initially, the correlation processor is in a standby mode with notarget information being processed.

2. Upon detection by the radar of enemy ECM activity, the SAM-D weaponssystem computer 47 supplies the correlator with estimates 45 and 46 ofthe jammers range and doppler position. These inputs are shown in FIG. 8to the delay line 21 (T) and to the voltage controlled crystaloscillator 19.

3. The doppler estimate 46 to the voltage controlled crystal oscillator(VCXO) 19 positions the jamming signal within the pass-band of thecorrelators bandpass filters.

4. The range estimate 45 positions the variable delay line 21 such thatthe jamming signal is within the range of acquisition of the range trackloop.

5. The doppler loop explained previously is shown outlined in FIG. 8.The input frequency from product detector is filtered by bandpass filter40 and applied to discriminator 41. If the frequency estimate had error,discriminator 41 forms an error voltage into integrator 43 whichre-positions VCXO 19 to exactly place the target frequency for maximumsignal. Within 0.2 to 0.3 seconds the doppler loop has achieved finalposition and the computer supplied estimate 46 is no longer used.

6. At the same time, the range loop, outlined in FIG. 8, is receivingsignal from the variable delay line and correlating it with signal fromthe missile in the pair of product detectors 28 and 28' and filters 29and 29'. If the range estimate was slightly in error, one of thesechannels of the pair will have a stronger output and will develop asignal to variable delay line 21 to correct the error. Within 0.2 to 0.3seconds the error is negligible, and the computer supplied estimate 45is not needed.

7. Should the jammer now move in range or doppler, the loops develop anerror signal to re-position the delay line and VCXO to always maximizethe signal of the jammer being tracked.

8. Once steady track has been established (0.2 to 0.3 seconds) delayline 21 and VCXO 19 are positioned such that the signals from theproduct detector 35 and 35 in the boresight angle section are maximized.These signals are filtered in band pass filters 36 and 36' and thenapplied to the two inputs of phase detector 38.

9. The phase detector output of the boresight angle section isintegrated by integrator 39. The phase detector output is a voltageproportional to the phase difference in the signals which (as is wellknown in the art) is in turn proportional to boresight angle, as thesignals originate in a monopulse antenna 7 (FIG. 1 Integrator 39 outputis the desired signal, since it contains information showing whether themissile is aiming at the jamming target.

10. The boresight error signal is fed to the weapon system computer 47shown in FIG. 1. Any error in aiming produces a voltage at the boresightchannel output which is used by the weapon system computer to generatenew steering commands to the missile by way of antenna 49 to correct theerror.

We claim:

1. Correlator system comprising at least one signal generator means;first, second, and third receiving means; said first receiving meansbeing located spacially from said second and third receiving means;transmitting means on said first receiving means; said first receivingmeans receiving signals from said signal generating means andtransmitting them to said second receiving means; said third receivingmeans receiving the signals generated by said signal generating means; avariable delay line; first mixer means having first and second inputsand an output; an output of said third receiving means connected throughsaid variable delay line to one of the inputs of said mixer means; anoutput of said second receiving means being connected to the other inputof said mixer means; said variable delay line having a controlled input;further comprising a range control loop connected between the output ofsaid variable delay line and said controlled input; said range controlloop comprising first and second channels;

each channel having a product detector which has first and secondinputs; each product detector having the signal from said secondreceiving means connected to the first input; a delay line connectedbetween the output of the variable delay line and the other input ofsaid product detector in said first channel; the other input of theproduct detector in said second channel being connected directly to theoutput of said variable delay line; a differential amplifer having firstand second inputs and an output; the outputs of said product detectorsbeing connected to different inputs of said differential amplifier; andthe output of the differential amplifier being connected to thecontrolled input of said variable delay line.

2. Correlator system comprising at least one signal generator means;first, second, and third receiving means; said first receiving meansbeing located spacially from said second and third receiving means;transmitting means on said first receiving means; said first receivingmeans receiving signals from said signal generating means andtransmitting them to said second receiving means; said third receivingmeans receiving the signals generated by said signal generating means; avariable delay line; first mixer means having first and second inputsand an output; an output of said third receiving means connected throughsaid variable delay line to one of the inputs of said mixer means; anoutput of said second receiving means being connected to the other inputof said mixer means; said first receiving means containing a monopulseradar receiver; said first receiving means having first and secondoutputs which are transmitted to said second receiving means; first andsecond channels; said second receiving means sending the first andsecond outputs of said first receiving means to said first and secondchannels respectively; said first channel being the connection to saidfirst mixer means; a second mixer means having two inputs and an output;the first input of said second mixer means being connected to the secondoutput of said second receiving means; said variable delay line beingconnected to the second input of said second mixer means; a phasedetector having two inputs and an output; and the output of said firstand second mixer means being connected to different inputs of said phasedetector.

3. A system as set forth in claim 2 wherein first and second delay linesare connected between said first and second outputs of said secondreceiving means and the mixer means.

4. A system as set forth in claim 3 wherein said variable delay line hasa controlled input; and further comprising a range control loopconnected between the output of said variable delay line and itscontrolled input.

5. A system as set forth in claim 4 further comprising third, fourth,and fifth mixer means; a local oscillator; said third, fourth, and fifthmixer means each having two inputs and an output; the first output ofsaid second receiving means being connected to one input of said thirdmixer means; the second output of said second receiving means beingconnected to one input of said fourth mixer means; said local oscillatorbeing connected to the other input of each of the said third and fourthmixer means; the output of said third mixer means being connected to aninput of said first mixer means; the output of said fourth mixer meansbeing connected to an input of said second mixer means; a

voltage control oscillator having an output and a con- 6. A system asset forth in claim wherein said signal trolled input; abandpass filter;a discriminator; an mtegenerators Consist f a plurality f jamming targetgrator; said bandpass filter, discriminator, and integrator beingconnected in a series circuit between the output of said first mixermeans and the controlled input 5 of said voltage control oscillatorwhereby the output of 531d target meanssaid first mixer is maximized.

means; and said first receiving means is a missile means having amonopulse antenna to receive the signals from

1. Correlator system comprising at least one signal generator means;first, second, and third receiving means; said first receiving meansbeing located spacially from said second and third receiving means;transmitting means on said first receiving means; said first receivingmeans receiving signals from said signal generating means andtransmitting them to said second receiving means; said third receivingmeans receiving the signals generated by said signal generating means; avariable delay line; first mixer means having first and second inputsand an output; an output of said third receiving means connected throughsaid variable delay line to one of the inputs of said mixer means; anoutput of said second receiving means being connected to the other inputof said mixer means; said variable delay line having a controlled input;further comprising a range control loop connected between the output ofsaid variable delay line and said controlled input; said range controlloop comprising first and second channels; each channel having a productdetector which has first and second inputs; each product detector havingthe signal from said second receiving means connected to the firstinput; a delay line connected between the output of the variable delayline and the other input of said product detector in said first channel;the other input of the product detector in said second channel beingconnected directly to the output of said variable delay line; adifferential amplifer having first and second inputs and an output; theoutputs of said product detectors being connected to different inputs ofsaid differential amplifier; and the output of the differentialamplifier being connected to the controlled input of said variable delayline.
 2. Correlator system comprising at least one signal generatormeans; first, second, and third receiving means; said first receivingmeans being located spacially from said second and third receivingmeans; transmitting means on said first receiving means; said firstreceiving means receiving signals from said signal generating means andtransmitting them to said second receiving means; said third receivingmeans receiving the signals generated by said signal generating means; avariable delay line; first mixer means having first and second inputsand an output; an output of said third receiving means connected throughsaid variable delay line to one of the inputs of saiD mixer means; anoutput of said second receiving means being connected to the other inputof said mixer means; said first receiving means containing a monopulseradar receiver; said first receiving means having first and secondoutputs which are transmitted to said second receiving means; first andsecond channels; said second receiving means sending the first andsecond outputs of said first receiving means to said first and secondchannels respectively; said first channel being the connection to saidfirst mixer means; a second mixer means having two inputs and an output;the first input of said second mixer means being connected to the secondoutput of said second receiving means; said variable delay line beingconnected to the second input of said second mixer means; a phasedetector having two inputs and an output; and the output of said firstand second mixer means being connected to different inputs of said phasedetector.
 3. A system as set forth in claim 2 wherein first and seconddelay lines are connected between said first and second outputs of saidsecond receiving means and the mixer means.
 4. A system as set forth inclaim 3 wherein said variable delay line has a controlled input; andfurther comprising a range control loop connected between the output ofsaid variable delay line and its controlled input.
 5. A system as setforth in claim 4 further comprising third, fourth, and fifth mixermeans; a local oscillator; said third, fourth, and fifth mixer meanseach having two inputs and an output; the first output of said secondreceiving means being connected to one input of said third mixer means;the second output of said second receiving means being connected to oneinput of said fourth mixer means; said local oscillator being connectedto the other input of each of the said third and fourth mixer means; theoutput of said third mixer means being connected to an input of saidfirst mixer means; the output of said fourth mixer means being connectedto an input of said second mixer means; a voltage control oscillatorhaving an output and a controlled input; a bandpass filter; adiscriminator; an integrator; said bandpass filter, discriminator, andintegrator being connected in a series circuit between the output ofsaid first mixer means and the controlled input of said voltage controloscillator whereby the output of said first mixer is maximized.
 6. Asystem as set forth in claim 5 wherein said signal generators consist ofa plurality of jamming target means; and said first receiving means is amissile means having a monopulse antenna to receive the signals fromsaid target means.